Preferably, conventional office chairs are designed to provide significant levels of comfort and adjustability. Such chairs typically include a base which supports a tilt control assembly to which a seat assembly and back assembly are movably interconnected. The tilt control mechanism includes a back upright which extends rearwardly and upwardly and supports the back assembly rearwardly adjacent to the seat assembly. The tilt control mechanism serves to interconnect the seat and back assembly so that they may tilt rearwardly together in response to movements by the chair occupant and possibly to permit limited forward tilting of the seat and back. Further, such chairs typically permit the back to also move relative to the seat during such rearward tilting.
The back assembly of such office chairs may have a variety of constructions wherein one type of construction includes an annular back frame which defines an open interior in which the chair occupant's back is,supported. This central open area is enclosed by a suspension fabric which spans the opening and has the outer peripheral edge thereof affixed to the annular frame.
The back frame further has a section thereof rigidly connected to an upright of the chair. The upright is connected to a tilt control mechanism, which mechanism supports the seat assembly and governs rearward tilting of the upright. As such, the back assembly moves in combination with the upright when the occupant reclines within the chair.
It is an object of the invention to provide an office chair having a chair back arrangement which is improved relative to prior chair back constructions and specifically is improved relative to the attachment of a suspension fabric to the rigid back frame.
Therefore, the invention relates to an office chair and more particularly, to the construction of a chair back assembly and the process for stretching and attaching the suspension fabric to the back frame in a stretched condition.
The back assembly comprises an annular frame having a suspension fabric which spans the central opening of the back and has the periphery of the suspension fabric connected to the frame. The fabric is stretched over and wraps sidewardly and rearwardly about the frame edge so that the frame is wrapped in fabric.
To achieve this finished appearance, the frame is formed of two ring-like frame sections that are mated together in facing relation. The suspension fabric comprises a single layer of suspension material which has its peripheral edge first connected to one of the frame sections when the fabric is stretched to form a sub-assembly and then this sub-assembly is affixed to the other frame sections with the fabric periphery sandwiched therebetween.
To form a peripheral channel for receipt of the fabric edge, the back frame is constructed of molded front and back rings which define the two frame sections. A thin groove is defined about their common peripheries in which groove the peripheral edge of the fabric is secured.
The front and rear ring sections overlie each other in opposing relation and are rigidly secured together by suitable fastening means such as ultrasonic welding, adhesives or even threaded fasteners. In this manner, complex contours may be formed in a molded back frame while still permitting the formation of a securement channel about the periphery thereof.
Before the frame is assembled, the suspension fabric is first fastened to one of the ring sections and preferably the front ring section by securement means such as ultrasonic welding. This fabric is pre-stretched during assembly and then secured to the front ring section before the front ring section is affixed to the rear ring section.
The process involves securing the fabric to the frame in a stretched condition, wherein an edge portion is released and secured to the frame while the major interior portion of the fabric is held in the stretched condition against the ring section. This is accomplished by stretching the fabric through a group of peripheral clamp assemblies which are all displaceable for such stretching of the fabric.
Once stretched, the ring section is positioned against a clamping body above the stretched fabric. The clamping body then moves the ring section downwardly against the fabric while the fabric is then pressed downwardly against a bottom nest which clamps the fabric between the bottom nest and the exterior face of the ring section. This clamps the fabric in a stretched condition, and the clamps are removed thereby leaving the peripheral edge of the fabric loose and projecting outwardly of the frame. The fabric is then wrapped over the edge of the ring section and secured to the interior ring face by suitable attachment means such as ultrasonic welding or even mechanical fasteners.
Thereafter, the clamping body is lifted, and the ring/fabric sub-assembly is ultrasonically welded to the rear ring section to define a composite chair frame with a suspension fabric.
The foregoing features provide an improved back frame arrangement, wherein other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience and reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the arrangement and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.